Expand padding while scroll

Solution.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Expanded scroll demo',
      theme: ThemeData.dark(),
      home: const Home(),
    );
  }
}

class Home extends StatelessWidget {
  const Home({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Example'),
      ),
      body: Column(
        children: [
          ElevatedButton(
            onPressed: () => SettingsPage.show(context, 100),
            child: Text('Long settings'),
          ),
          ElevatedButton(
            onPressed: () => SettingsPage.show(context, 5),
            child: Text('Small settings'),
          ),
        ],
      ),
    );
  }
}

class SettingsPage extends StatelessWidget {
  const SettingsPage({
    Key? key,
    required this.tileCount,
  }) : super(key: key);

  final int tileCount;

  static Future<void> show(BuildContext context, int tileCount) {
    return Navigator.push(
      context,
      PageRouteBuilder(
        opaque: false,
        barrierDismissible: true,
        barrierColor: Colors.black38,
        pageBuilder: (context, anim1, anim2) => SlideTransition(
          position: Tween(
            begin: const Offset(0, 1),
            end: Offset.zero,
          ).animate(
            CurvedAnimation(
              parent: anim1,
              curve: Curves.easeOut,
            ),
          ),
          child: SettingsPage(
            tileCount: tileCount,
          ),
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    final mediaQuery = MediaQuery.of(context);
    return ExpandedScrollContainer(
      builder: (context, controller) => Material(
        child: CustomScrollView(
          controller: controller,
          shrinkWrap: true,
          physics: ClampingScrollPhysics(),
          slivers: [
            SliverAppBar(
              pinned: true,
              leading: IconButton(
                icon: Icon(Icons.close),
                onPressed: () => Navigator.pop(context),
              ),
              title: Text(
                'Settings',
              ),
            ),
            SliverPadding(
              padding: mediaQuery.padding.copyWith(top: 0),
              sliver: SliverList(
                delegate: SliverChildListDelegate(
                  [
                    for (var i = 0; i < tileCount; i++)
                      ListTile(
                        title: Text('Tile $i'),
                      ),
                  ],
                ),
              ),
            )
          ],
        ),
      ),
    );
  }
}

class SettingsBar extends StatelessWidget {
  const SettingsBar({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final mediaQuery = MediaQuery.of(context);
    return Padding(
      padding:
          mediaQuery.padding.copyWith(bottom: 0) + const EdgeInsets.all(10),
      child: IconButton(
        icon: Icon(
          Icons.close,
        ),
        onPressed: () => Navigator.pop(context),
      ),
    );
  }
}

typedef AnimatedScrollWidgetBuilder = Widget Function(
  BuildContext context,
  ScrollController controller,
);

class ExpandedScrollContainer extends StatefulWidget {
  const ExpandedScrollContainer({
    Key? key,
    required this.builder,
    this.initialBorderRadius = const BorderRadius.all(Radius.circular(10)),
    this.removePaddingExtentOffset = 200.0,
    this.initialPadding = const EdgeInsets.only(
      left: 20,
      right: 20,
      top: 60,
    ),
  }) : super(key: key);

  final BorderRadius initialBorderRadius;
  final EdgeInsets initialPadding;
  final double removePaddingExtentOffset;
  final AnimatedScrollWidgetBuilder builder;

  @override
  _ExpandedScrollContainerState createState() =>
      _ExpandedScrollContainerState();
}

class _ExpandedScrollContainerState extends State<ExpandedScrollContainer> {
  final ScrollController controller = ScrollController();

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final mediaQuery = MediaQuery.of(context);
    final totalPadding = mediaQuery.padding + widget.initialPadding;
    return Dismissible(
      key: Key('Dismiss'),
      direction: DismissDirection.down,
      onDismissed: (_) => Navigator.pop(context),
      child: AnimatedBuilder(
        animation: controller,
        builder: (context, _) {
          final offset = controller.hasClients
              ? controller.offset
              : controller.initialScrollOffset;
          print(offset);
          final amount =
              (offset / widget.removePaddingExtentOffset).clamp(0.0, 1.0);
          return Align(
            alignment: Alignment.bottomCenter,
            child: Padding(
              padding: EdgeInsets.lerp(
                totalPadding.copyWith(bottom: 0),
                EdgeInsets.zero,
                amount,
              )!,
              child: ClipRRect(
                borderRadius: BorderRadius.lerp(
                  widget.initialBorderRadius,
                  BorderRadius.zero,
                  amount,
                ),
                child: MediaQuery(
                  data: mediaQuery.copyWith(
                    padding: EdgeInsets.lerp(
                      mediaQuery.padding.copyWith(top: 0, left: 0, right: 0),
                      mediaQuery.padding,
                      amount,
                    )!,
                  ),
                  child: widget.builder(context, controller),
                ),
              ),
            ),
          );
        },
      ),
    );
  }
}